This application claims the priority of Korean Patent Application No. 2002-44462, filed on Jul. 27, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to perpendicular magnetic recording media, and more particularly, to a perpendicular magnetic recording medium with an increased recording density.
2. Description of the Related Art
Perpendicular magnetic recording media generally have high recording density, as compared to longitudinal magnetic recording mechanism. Hence, recent hard disk drives (HDDs) use perpendicular magnetic recording media to obtain a high recording density. Perpendicular magnetic recording media have a magnetization that is perpendicular to the-main plane of the media. The recording density of such perpendicular magnetic recording media is greatly affected by the properties of a perpendicular magnetic recording layer and by an underlayer which perpendicularly orients a magnetization in a magnetic recording layer.
FIG. 1 shows the layer structure of a conventional perpendicular magnetic recording medium having a single magnetic layer. FIGS. 2 and 3 show the later structures of conventional perpendicular magnetic recording media having two magnetic layers.
Referring to FIG. 1, a perpendicular magnetic recording layer 13, where information is recorded, is placed over the upper surface of a substrate 11. A perpendicular orientation underlayer 12 for perpendicularly orienting the magnetization of the perpendicular magnetic recording layer 13 is placed between the substrate 11 and the perpendicular magnetic recording layer 13. A protection layer 14 is formed on the perpendicular magnetic recording layer 13 to protect the perpendicular magnetic recording layer 13. A lubricating layer 15 is formed on the protection layer 14 to reduce abrasion of a magnetic head of an HDD and the protection layer 14 due to collision and sliding of the protective layer 14 and the magnetic head.
Referring to FIG. 2, a perpendicular magnetic recording layer 23, where information is recorded, is placed over the upper surface of a substrate 21. A soft material layer 22, which forms a magnetic path of a perpendicular magnetic field generated by a magnetic head of an HDD, is placed between the substrate 21 and the perpendicular magnetic recording layer 23. A protection layer 24 and a lubricating layer 25 are sequentially formed on the perpendicular magnetic recording layer 23.
Referring to FIG. 3, a perpendicular magnetic recording layer 224, where information is recorded, is placed over the upper surface of a substrate 221. A perpendicular orientation underlayer 223 and a soft material layer 222 are placed between the substrate 221 and the perpendicular magnetic recording layer 224. A protection layer 225 and a lubricating layer 226 are sequentially formed on the perpendicular magnetic recording layer 224.
The types and composition ratio of elements that form each of the perpendicular magnetic recording layers 13, 23, and 224 greatly affect the types and structures of the corresponding perpendicular orientation underlayers 12 and 223 and the soft magnetic layer 22. An existing perpendicular orientation underlayer formed of Ti or Pt is greatly affected by the characteristics of a perpendicular magnetic recording layer. If a perpendicular orientation underlayer is formed of Ti, a thick initial growth film is formed between the perpendicular magnetic layer and the Ti perpendicular orientation underlayer due to the difference in the crystal lattice constant between them. Thus, the orientation characteristic of the perpendicular magnetic recording layer is deteriorated. A perpendicular orientation underlayer formed of Pt has an excellent perpendicular crystal orientation because it has a small difference in the lattice constant from the perpendicular magnetic recording layer. However, the excellent perpendicular crystal orientation shown in some perpendicular magnetic recording layers causes crystal grains to be enlarged and exchanged coupling to be increased, thereby degrading a signal-to-noise ratio (SNR) upon information recording/writing.